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What is SIP?

By: Tim Wallhurst

A lot of IP devices are built with SIP interoperability—and manufacturers are quick to let you know about it. "SIP" is a popular term to throw around because it carries a lot of authority. So why's it so popular and what is it?

SIP is a protocol that establishes rules for how IP devices communicate. One reason that this protocol is popular for VoIP communications is because SIP was originally designed to mimic how analog telephony functions. Since then, it has grown to support a wider variety of IP-based features, including video communications.

SIP is an acronym for "Session Initiation Protocol." A "SIP session" uses this protocol's rules for sending and receiving signals over an IP network. A "SIP user agent" is the endpoint, such as a phone or other telephony device.

Basically, SIP lays the groundwork for how IP devices establish a call, terminate the call, and other basic elements. While SIP includes support for many features, the PBX, phone and other equipment may not be compatible with all SIP-enabled telephony functions.

SIP Compatibility

An endpoint with SIP compatibility should work on a SIP-based phone system. However, if the endpoint does not support SIP, then it will not work with a SIP-only phone system.

Compatibility is key, otherwise the powerful telephony features that SIP offers are worthless to your endpoints or phone system.

Fortunately, SIP is an extremely popular protocol. It has become a standard for how IP devices communicate. Other protocols exist, but a majority of IP devices will carry SIP interoperability. Even proprietary phone systems and endpoints will sometimes support SIP.